1. Field of the Invention
The invention relates to an optical measurement system, a measurement method for errors of a rotating platform, and a two-dimensional sine wave annulus grating.
2. Description of Related Art
Rotating platforms are key instruments in the equipment for middle and high level manufacturing processes, and are broadly used in high-precision industrial processes, such as ultra-precision manufacturing and/or processing and opto-electronic semiconductor manufacturing processes. Currently, the accuracy of the rotating platform is inspected by testing the geometric precision and positioning precision of the rotating platform by using a measurement instrument such as the laser interferometer, the autocollimator, or the electronic level meter, etc. Since these instruments are adapted for off-line measurements, and correction processes are respectively required for installation of these instruments and alignment of the reference shaft, the current process for correcting the rotating platform is very time-consuming. In addition, since measurement paths measured when correcting the rotating platform may not be completely identical, errors may be introduced through multiple correction processes. The uncertainty of measurement is thus increased. Furthermore, when inspecting the accuracy of the rotating platform, the operation of the manufacturing equipment (e.g., the machine tool) must be suspended, which results in decrease in production. Thus, measuring the errors of the rotating platform in real-time on the production line will significantly help the precision correction process of the rotating platform.